A method for synthesizing and purifying p-hydroxybenzoic acid
By using a hydrogenation catalyst to perform the reduction reaction during the synthesis of parahydroxybenzoic acid, combined with the separation step of acidic aqueous solution, the problem of difficulty in purification of parahydroxybenzoic acid in the prior art is solved, and a high-purity and colorless product is achieved Preparation reduces production costs and waste liquid pollution.
Patent Information
- Application Number
- CN202311668742.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-07
- Publication Date
- 2025-02-11
- Estimated Expiration
- 2043-12-07
Smart Images
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Abstract
Description
Technical Field
[0001] The invention belongs to the field of organic synthesis, and particularly relates to a method for synthesizing and purifying p-hydroxybenzoic acid. Background Art
[0002] The traditional conventional synthesis process is generally carried out through the following process:
[0003] In a stainless steel kettle, add the carbonized p-hydroxybenzoic acid dipotassium salt solution, then add hydrosulfite and activated carbon, and then heat to 90°C, stir and decolorize at 90°C for 30 minutes, filter out the activated carbon, and obtain a light wine (brown) red transparent solution, add acid to adjust the pH value to 6.5-8.0, cool to 40-60°C, separate the precipitated solid potassium salt by filtration, and continue to acidify the obtained mother liquor to pH 2.0-4.0, and a large amount of light yellow p-hydroxybenzoic acid product precipitates, cool to 25°C, separate by filtration, and obtain a light yellow solid product. After drying, the chromaticity is 40-60 Hazen, and the transmittance at 425nm is 73.5-82.5%. It does not meet the quality standard requirements of industrial qualified products. It needs to be prepared by water recrystallization, resulting in a large amount of waste liquid, polluting the environment and increasing production costs.
[0004] For example, in patent application 201210056215.6, potassium hydroxide solution and phenol are reacted in a salt-forming reactor to obtain potassium salt of phenol, and then carbon dioxide is introduced into a carboxylation reactor for carboxylation reaction to obtain a potassium salt aqueous solution of p-hydroxybenzoic acid, which is then decolorized with activated carbon, acidified with sulfuric acid, and finally filtered, washed with water, and dried to obtain the product; the above process is repeated to obtain a p-hydroxybenzoic acid product with a chromaticity of less than 20 Hazen.
[0005] As a very important intermediate in the chemical industry, p-hydroxybenzoic acid can be used as a preservative, dye, medicine and injection molding intermediate. It can be esterified with alcohol to obtain parabens. It is also the main raw material of high molecular liquid crystal polymers and the raw material of pesticide intermediates. Especially when used to prepare high molecular liquid crystal polymers, high chromaticity and impurities have a great impact on the yield of liquid crystals. At this time, high-purity colorless and transparent p-hydroxybenzoic acid is required as a raw material.
[0006] Therefore, there is an urgent need in the art for a method for purifying p-hydroxybenzoic acid with simple operation and low cost, especially for removing impurity color and improving product purity. Summary of the invention
[0007] In view of the shortcomings of the prior art, the present invention provides a method for synthesizing and purifying p-hydroxybenzoic acid, which is simple to operate, low-cost, green and pollution-free. After analysis, it is found that the substance producing wine (brown) red is phenol that is inevitably oxidized during the high-temperature salt formation and carboxylation reaction process, producing benzoquinone-like colored substances. The applicant has found and verified through experiments that the hydrogenation reaction of a hydrogenation catalyst can reduce benzoquinone to a colorless phenol substance, and then separate the system according to the solubility properties of potassium sulfate in an acidic aqueous solution.
[0008] To achieve the above object, the present invention adopts the following technical solutions:
[0009] S1: In a reactor, add a carboxylated p-hydroxybenzoic acid dipotassium salt aqueous solution, then add a hydrogenation catalyst, and remove the air in the reactor with an inert gas;
[0010] S2: heating and stirring, then introducing hydrogen to replace the internal pressure to 0.2-1.5MPa, observing the reactor until no hydrogen is absorbed in the reactor, which is the end point;
[0011] S3: Cooling the reactor, exhausting the hydrogen in the reactor with inert gas, and separating the hydrogenation catalyst from the solution to obtain a nearly colorless transparent solution;
[0012] S4: adding acid to the nearly colorless transparent solution to adjust the pH to 6.0-8.0, and continuing to cool to 30-60°C to precipitate solid potassium salt;
[0013] S5: The mother liquor obtained by filtration separation is further adjusted to pH 2.0-4.0 with acid, at which time a white p-hydroxybenzoic acid product is precipitated; the mother liquor is cooled, filtered and separated, and dried to obtain a white product.
[0014] Preferably, the aqueous solution of dipotassium salt of p-hydroxybenzoic acid in step S1 is wine / maroon, with a chromaticity greater than 300 Hazen; the inert gas is nitrogen;
[0015] Preferably, the hydrogenation catalyst comprises at least one of Raney nickel, palladium carbon, and palladium aluminum;
[0016] Preferably, the mass volume ratio of the hydrogenation catalyst to the aqueous solution of dipotassium salt of p-hydroxybenzoic acid is 0.002-0.008:1 g / mL.
[0017] Preferably, in step S2, the pressure of the reactor is 0.5-1.5 MPa, and the programmed temperature is 80-100°C.
[0018] Preferably, in step S3, the temperature is lowered to 60-80° C.; the inert gas is nitrogen, and the hydrogenation catalyst separated by filtration is recovered and reused.
[0019] Preferably, in step S4, the pH value is 6.5-8.0, and the temperature is lowered to 40-60°C.
[0020] Preferably, the acid used in step S4 is 20-40% sulfuric acid, and the potassium salt is potassium sulfate.
[0021] Preferably, in step S5, the temperature is lowered to room temperature; the pH value is adjusted to 2.5-4.0; and the acid used is 20-40% sulfuric acid.
[0022] Preferably, the chromaticity of the white product after drying in step S5 is 0-10 Hazen, and the transmittance at 425 nm reaches 96.2-98%.
[0023] Preferably, the hydrogenation catalyst in step S3 is recycled 20-30 times.
[0024] Preferably, the equation for the acidification process in step S4 is as follows:
[0025]
[0026] Acidification in step S5:
[0027]
[0028] The preparation of p-hydroxybenzoic acid dipotassium salt solution is obtained by the following steps:
[0029] A1: Add phenol to a reaction kettle and heat to melt, add potassium hydroxide powder, stir and heat to 220-250°C, react to obtain molten potassium phenolate, and remove water in vacuo;
[0030] Preferably, the heating and melting temperature in step A1 is 50-65°C; the temperature is raised to 230-250°C; and the mass ratio of phenol to potassium hydroxide is 1:0.90-1.10.
[0031] Preferably, the reaction time in step A1 is 30-100 minutes.
[0032] A2: Carbon dioxide was introduced into the above reactor to carry out carboxylation reaction. After a period of reaction, the reaction was stopped.
[0033]
[0034] reaction;
[0035] Preferably, the flow rate of carbon dioxide in step A2 is 300-500 mL / min, and the reaction time is
[0036]
[0037] 60-150 minutes.
[0038] A3: Cool the above step to 200-230° C., distill off phenol to obtain solid p-hydroxybenzoic acid dipotassium salt, and add distilled water to obtain the above p-hydroxybenzoic acid dipotassium salt aqueous solution.
[0039] Preferably, the temperature in step A3 is reduced to 200-220°C.
[0040] Beneficial effects of the present invention:
[0041] 1) The hydrogenation catalyst can be applied at least 20 times and has good reduction selectivity for quinones; 2) It reduces the adsorption of activated carbon to the product, improves the yield, reduces the generation of solid waste, avoids the use of organic solvents for recrystallization, reduces the generation of waste liquid, and has lower production costs; 3) Hydrogenation reduction in water systems is highly safe; 4) The product appearance color is better than that of insurance powder and activated carbon, and the product color is 0-10 Hazen, which meets the standards and specifications of subsequent products.
[0042] The invention can solve the similar problems of high cost and the like by improving the synthesis process, and achieve the effects of increased yield, improved qualified rate and better reaction effect. DETAILED DESCRIPTION
[0043] The present invention is further described below by means of specific examples, but the scope of the present invention is not limited thereto.
[0044] Example 1: Preparation of dipotassium p-hydroxybenzoate
[0045] 300 g of phenol was added to a 1000 mL autoclave with a stirring device, and heated to 60°C until it melted. Then 280 g of potassium hydroxide powder was added, and the mixture was stirred and heated to 80°C to remove water under reduced pressure. The mixture was then heated to 240°C. After 60 minutes of reaction, molten potassium phenolate was obtained, and the water produced in the reactor was removed in vacuo.
[0046] Use a high-purity carbon dioxide cylinder to pass CO2 into the reactor for carboxylation reaction, and control the flow rate at 300mL / min. After 100 minutes of reaction, close the cylinder valve to stop the reaction;
[0047] The reaction kettle was cooled to about 200°C, and the phenol produced by the reaction was distilled off to obtain 455 g of solid p-hydroxybenzoic acid dipotassium salt. 430 g of distilled water was added to obtain a wine (brown) red p-hydroxybenzoic acid dipotassium salt aqueous solution. The solution was cooled to room temperature and the chromaticity was measured to be 330 Hazen, which was used in the following examples.
[0048] Example 2: Preparation of p-hydroxybenzoic acid
[0049] In a 1000mL autoclave, 300mL of the aqueous solution of dipotassium p-hydroxybenzoate in Example 1 was introduced, 0.5g of Raney nickel was added, nitrogen was introduced to replace the air in the reactor, the reaction mixture was stirred rapidly, and the reaction mixture was heated to about 90°C. At this time, hydrogen was introduced into the autoclave to maintain the pressure in the autoclave at 1.0MPa until no hydrogen was absorbed.
[0050] The temperature was lowered to about 60°C, and the hydrogen in the autoclave was evacuated with nitrogen. The Raney nickel was separated by filtration and reserved for next use. The obtained colorless transparent aqueous solution was adjusted to pH 6.5 by adding 30% dilute sulfuric acid, and the temperature was further lowered to 45°C. 16 g of solid potassium sulfate was precipitated.
[0051] Solid potassium sulfate was separated by filtration to obtain 450 g of mother liquor, and the mother liquor was further adjusted to pH 2.5 with 30% dilute sulfuric acid. At this time, white p-hydroxybenzoic acid product was precipitated. Wait until no solid precipitated; cool to about 30° C., filter and separate, and dry to obtain 28 g of a white product, which is p-hydroxybenzoic acid with a chromaticity of 8 Hazen.
[0052] The recovered Raney nickel is reused, and a small amount of lost Raney nickel needs to be replenished later. It can be reused at least 20 times.
[0053] Example 3: Preparation of p-hydroxybenzoic acid
[0054] In a 1000mL autoclave, introduce 300mL of the aqueous solution of dipotassium p-hydroxybenzoate in Example 1, add 1g of 0.5% palladium carbon Pb / C, introduce nitrogen to replace the air in the reactor, stir rapidly, and heat to about 80°C. At this time, introduce hydrogen into the autoclave to maintain the pressure in the autoclave at 0.5MPa until no hydrogen is absorbed.
[0055] The temperature was lowered to about 65°C, and the hydrogen in the autoclave was evacuated with nitrogen. The palladium carbon was separated by filtration and reserved for next use. The obtained colorless transparent aqueous solution was adjusted to pH 6.6 by adding 30% dilute sulfuric acid, and the temperature was further lowered to 45°C. 17 g of solid potassium sulfate was precipitated.
[0056] Solid potassium sulfate was separated by filtration to obtain 448 g of mother liquor. The mother liquor was further adjusted to pH 2.5 with 30% dilute sulfuric acid. At this time, white p-hydroxybenzoic acid product began to precipitate. Wait until no solid precipitated; cool to room temperature, filter and separate, and dry to obtain 27.5 g of a white product, which is p-hydroxybenzoic acid with a chromaticity of 6 Hazen.
[0057] The recovered palladium-on-carbon can be recycled again with almost no need for replenishment and can be reused at least 20 times.
[0058] Example 4: Preparation of p-hydroxybenzoic acid
[0059] In a 1000mL autoclave, introduce 300mL of the aqueous solution of dipotassium p-hydroxybenzoate in Example 1, add 1g of 0.5% palladium aluminum Pb / Al, introduce nitrogen to replace the air in the reactor, stir rapidly, and heat to about 80°C. At this time, introduce hydrogen into the autoclave to maintain the pressure in the autoclave at 0.5MPa until no hydrogen is absorbed.
[0060] The temperature was lowered to about 60°C, and the hydrogen in the autoclave was evacuated with nitrogen. The palladium aluminum was separated by filtration and kept for next use. The obtained colorless transparent aqueous solution was adjusted to pH 6.7 by adding 30% dilute sulfuric acid, and the temperature was further lowered to 45°C. 17.3 g of solid potassium sulfate was precipitated.
[0061] Solid potassium sulfate was separated by filtration to obtain 451 g of mother liquor, and the pH value of the mother liquor was further adjusted to 2.5 with 30% dilute sulfuric acid. At this time, white p-hydroxybenzoic acid product began to precipitate. Wait until no solid precipitated; cool to room temperature, filter and separate, and dry to obtain 28.2 g of a white product, which is p-hydroxybenzoic acid, with a chromaticity of 8 Hazen.
[0062] The recovered palladium aluminum can be recycled again with almost no need for replenishment and can be reused at least 20 times.
[0063] Example 5: Pilot scale preparation of p-hydroxybenzoic acid
[0064] In a 500L reactor with a stirring device, 120KG of potassium hydroxide powder and 128.5KG of phenol were added and heated to 65°C until melted. At the same time, the mixture was stirred and heated to 170°C and the water was slowly removed by decompression. The mixture was then heated to 240°C. After 2 hours of reaction, molten potassium phenolate was obtained and the water produced in the reactor was removed by vacuum.
[0065] Open the high-purity carbon dioxide cylinder and introduce CO2 into the reactor for carboxylation reaction. The flow rate is controlled at 30L / min. After 120 minutes of reaction, close the cylinder valve, reduce the pressure to remove phenol until it is completely removed, and stop the reaction;
[0066] The reactor was cooled to about 130°C, 200 kg of purified water was pumped in, and a wine (brown) red aqueous solution of p-hydroxybenzoic acid dipotassium salt was obtained under stirring, which was then cooled to 80°C and transferred to another 500 L autoclave.
[0067] Add 2.5 kg of 0.5% palladium carbon Pb / C, introduce nitrogen to replace the air in the reactor, stir rapidly, and heat to about 80°C. At this time, introduce hydrogen into the autoclave to maintain the pressure in the autoclave at 0.5 MPa until no hydrogen is absorbed.
[0068] The temperature was lowered to about 60°C, and the hydrogen in the autoclave was evacuated with nitrogen. The palladium carbon was separated by filtration and kept for next use. The colorless transparent aqueous solution was adjusted to pH 6.0 by adding 30% dilute sulfuric acid, and the temperature was further lowered to 50°C. 53KG of solid potassium sulfate was precipitated.
[0069] Solid potassium sulfate was separated by filtration, and the pH value of the obtained mother liquor was adjusted to 2.5 with 30% dilute sulfuric acid. At this time, white p-hydroxybenzoic acid product was precipitated. Wait until no solid precipitated; cool to room temperature, filter and separate, and dry to obtain a white product, i.e. p-hydroxybenzoic acid, with a chromaticity of 7 Hazen.
[0070] Comparative Example 1:
[0071] In a 1000mL autoclave, add 300mL of the p-hydroxybenzoic acid dipotassium salt solution in Example 1, then add 1g of hydrosulfite and 3g of activated carbon, and then heat to 90°C, stir and decolorize at 90°C for 30 minutes, filter out the activated carbon, and obtain a light wine (light brown) red transparent solution with a chromaticity of 86 Hazen. Add 30% dilute sulfuric acid to adjust the pH value to 6.8, cool to 45°C, separate 17g of the precipitated solid potassium sulfate salt by filtration, and the obtained mother liquor is further acidified to pH 2.4 with 30% dilute sulfuric acid, and a large amount of light yellow p-hydroxybenzoic acid product is precipitated. Cool to 30°C, separate by filtration, and obtain 33.3g of a light yellow solid product. After drying, obtain 26.5g of a light yellow gray solid product with a chromaticity of 43 Hazen and a transmittance of 81.5% at 425nm. Use 80mL of purified water for recrystallization to prepare a product with a chromaticity of 8 Hazen.
[0072] The above-mentioned embodiments only express several preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.
Claims
1. A method for synthesizing and purifying p-hydroxybenzoic acid, characterized in that: The steps include: S1: In a reactor, add a carboxylated p-hydroxybenzoic acid dipotassium salt aqueous solution, then add a hydrogenation catalyst, and remove the air in the reactor with an inert gas; S2: heating and stirring, then introducing hydrogen to replace the internal pressure to 0.2-1.5MPa, observing the reactor until no hydrogen is absorbed in the reactor, which is the end point; S3: Cooling the reactor, exhausting the hydrogen in the reactor with inert gas, and separating the hydrogenation catalyst from the solution to obtain a nearly colorless transparent solution; S4: adding acid to the nearly colorless transparent solution to adjust the pH to 6.0-8.0, and continuing to cool to 30-60°C to precipitate solid potassium salt; S5: The mother liquor obtained by filtration separation is further adjusted to pH 2.0-4.0 with acid, at which time a white p-hydroxybenzoic acid product is precipitated; the mother liquor is cooled, filtered and separated, and dried to obtain a white product.
2. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: The carboxylated p-hydroxybenzoic acid dipotassium salt solution is obtained by the following steps: A1: Phenol is added to a reaction kettle and heated to melt, potassium hydroxide powder is added, water is removed under reduced pressure, and the temperature is raised while stirring to obtain molten potassium phenolate. After reacting for a period of time, the reaction is stopped and water is removed under vacuum; A2: introducing carbon dioxide into the above reactor to carry out carboxylation reaction, and stopping the reaction after reacting for a period of time; A3: Cool the above step to 200-230° C., distill off phenol to obtain solid p-hydroxybenzoic acid dipotassium salt, and add distilled water to obtain the above p-hydroxybenzoic acid dipotassium salt aqueous solution.
3. A method for synthesizing and purifying p-hydroxybenzoic acid according to claim 2, characterized in that: The heating and melting temperature in step A1 is 50-65°C; the temperature is raised to 230-250°C; the mass ratio of phenol to potassium hydroxide is 1:0.9-1.1; the reaction time in step A1 is 30-100 minutes; The flow rate of carbon dioxide in step A2 is 300-500 mL / min, and the reaction time is 60-150 minutes; The temperature in step A3 is reduced to 200-220°C.
4. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: In step S1, the dipotassium salt of p-hydroxybenzoic acid solution is wine red or brown red; the inert gas is nitrogen; and the hydrogenation catalyst includes at least one of Raney nickel, palladium carbon, and palladium aluminum.
5. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: In step S2, the pressure of the reactor is 0.5-1.5 MPa; the programmed temperature is 80-100°C.
6. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: In the step S3, the temperature is lowered to 60-85° C.; the inert gas is nitrogen.
7. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: In step S4, the pH value is 6.5-8.0, and the temperature is lowered to 40-60° C.; the acid is sulfuric acid with a concentration of 20-40%, and the potassium salt is potassium sulfate.
8. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: In the step S5, the temperature is lowered to room temperature; the pH value is adjusted to 2.5-4.0; and the acid is sulfuric acid with a concentration of 20-40%.
9. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: The white product after drying in step S5 has a chromaticity of 0-10 Hazen and a transmittance of 96.2-98% at 425 nm.
10. The method for synthesizing and purifying p-hydroxybenzoic acid according to claim 1, characterized in that: The hydrogenation catalyst in step S3 is recycled 20 to 30 times.